Antibodies to membrane antigens of cells infected by varicella-zoster virus were detected by immunofluorescence. Rises in varicella-zoster IgA, IgG, and IgM were detected after both varicella and zoster. Prompt antibody responses were observed in patients with generalized zoster as well as in those with localized zoster. A delayed response was found, moreover, in one patient who did not develop disseminated disease. Antibody to varicella-zoster virus was detected in the sera of all three patients tested prior to and in all but one of 63 patients tested soon after onset of zoster, The level of varicella-zoster IgA and IgG rose in two of three immune patients after household exposure to infection with varicella-zoster virus, Varicella-zoster IgG was detected in the cord blood of infants whose mothers were immune to varicella.